This invention relates to a process for synthesizing silanol chain-stopped polysiloxane fluids and is particularly related to a process for producing silanol chain-stopped fluorosilicone polymers.
Fluorosilicone compositions offer unique properties which perform well in hostile environments and meet such industrial requirements as fuel and solvent resistance. Fluorosilicones retain all the inherent temperature stability and good electrical and thermal properties of other silicones and remain strong, resilient and flexible at high and low temperature extremes where many organic elastomers fail. Fluorosilicone polymers can impart these advantages to otherwise conventional silicone products such as greases and hydraulic fluids. Fluorosilicone gums can be made into fluorosilicone rubbers of both the heat cured, and room temperature vulcanizable varieties. Cured fluorosilicone elastomers will then exhibit the aforementioned desirable properties such as solvent resistance.
Among the many possible fluoro-substituted diorganopolysiloxane compositions, it has been found that silanol chain-stopped fluoroalkylpolysiloxanes are particularly useful and valuable silicone fluids. Among these, the silanol stopped methyl trifluoropropyl polysiloxane fluids are especially valuable.
The present invention provides a novel process for producing such fluids in high yield while minimizing the production of undesirable byproducts such as volatile cyclic siloxanes. Such fluorosilicone fluids are normally utilized in either of two ways. Silanol chain-stopped fluorosiloxane polymers can be a basic ingredient in a condensation-cure fluorosilicone RTV-type product. On the other hand, as described in my copending application filed concurrently herewith, these silanol chain-stopped fluorosiloxane polymers can be treated with trimethylchlorosilane to produce a trimethyl chain-stopped fluoro-substituted dialkyl polysiloxane. This product is known as an M-stopped fluorosilicone fluid and forms the basis for many fluorosilicone products such as greases and hydraulic fluids.
A previous attempt to produce silanol chain-stopped fluorosilicone polymers is described in U.S. Pat. No. 3,373,138, issued Mar. 12, 1968, to E. D. Brown, wherein linear and branched fluoroalkylpolysiloxanes are produced through the hydrolysis of halosilanes with a goal of avoiding the production of cyclic polysiloxanes. This is to distinguish from the present invention wherein silanol chain-stopped fluorosilicone polymers are produced directly from fluoro-substituted diorganotrisiloxanes rather than from halosilanes.
Alternatively, U.S.S.R. No. 238,780, Yuzhelevskii et al, patented July 8, 1965 and published Oct. 3, 1973, claims to provide a method for obtaining 3,3,3-trifluoropropyl polysiloxane diols by polymerizing 1,3,5-trimethyltris-(3,3,3-trifluoropropyl)-cyclotrisiloxane in the presence of water, a sodium hydroxide catalyst and a nitrogen and oxygen containing activating additive, such as for instance, nitriles or amides of acids, ketones, cyclic and linear ethers and cyanalkylsiloxanes. The disclosure, however, only teaches the use of acetone or cyanoalkyl (methyl) dichlorosilane in the production of polysiloxane diols and does not demonstrate that polysiloxane diols can be obtained in high yield with the use of a polyethylene glycol dimethyl ether type promoter.
In my copending application, Ser. No. 959,544, filed Nov. 13, 1978, Bluestein et al, which is hereby incorporated by reference, it is further shown that fluorosilicone polymers can be formed by reacting a cyclic siloxane trimer containing fluorine substituted hydrocarbon radicals with a low molecular weight, silanol chain-stopped polydiorganosiloxane in the presence of a basic catalyst. That application, however, is fundamentally different from the present invention wherein silanol chain-stopped fluorosilicone fluids are produced.
It is therefore an object of the present invention to provide a process for producing a silanol chain-stopped fluoro-substituted diorganopolysiloxane fluid and particularly a silanol chain-stopped methyltrifluoropropylsiloxane polymer.